I have presented the concept of the binocular symmetrical properties of stereoscopic image fields (paper given orally, SMPTE Technical Conference, Los Angeles, Oct. 20, 1977) and have elaborated on the idea in my book, FOUNDATIONS OF THE STEREOSCOPIC CINEMA (to be published by Van Nostrand Reinhold, 1982). Other workers, such as Norling (PSA Journal, Vol. 18, Jan. 1952) have understood the idea in the context of the present teaching, namely, of illumination symmetry.
The two projected stereoscopic image fields must be very much alike to specifiable tolerances in terms of abberation, illumination, geometry, color, registration, and temporal symmetry. The only desired difference is horizontal parallax, which is controlled at the time of photography and is directly responsible for the depth cue of stereopsis. I have found in the course of my research that departures from the symmetrical conditions enumerated above lead to viewer discomfort, and that this discomfort is generally referred to parts of the body other than the eyes. The various asymmetries are psychologically additive. Moreover, the effect of these disturbances are cumulative with time.
In the present disclosure I am concerned with projection and the control of illumination symmetry in order to minimize viewer discomfort. The method I employ is rapid, economical, and within the means of the average theatrical projectionist to employ successfully. Heretofore, such means have not been available.
The invention uses additive color for a visual comparison of the illumination intensity of left and right fields. I have searched the literature and can find no similar application of this technique. Gruber, in U.S. Pat. No. 2,700,322 describes an additive color technique for the alignment of lens axes in stereoscopic projection, so that additive color fringes might be observed if projected targets are not precisely in superimposition.
Culver, Maule, and Unterborg (IBM Technical Disclosure Bulletin, Vol. 17, No. 10, March 1975) describe a similar technique for alignment of parts.
However, the present disclosure is substantially different and is concerned with the calibration of illumination intensity.